The invention relates to monitoring arrangements for monitoring the operativeness of electrical devices.
Circuits are known for monitoring the operativeness of, for example, the tail lights of an automotove vehicle. In one known construction, use is made of ordinary relays. With ordinary relays, the difference between their pull-in and drop-out characteristics is relatively great, and it worsens over prolonged periods of use. A further disadvantage of the known construction is that circuits of that type do not provide an indication of the failure of a safety fuse. Also, such ordinary relays, because of their moving parts, are sensitive to moisture, temperature, dust and vibration. Additionally, the relatively large number of turns in the windings of such relays result in an undesirably large voltage drop.
Other monitoring circuits incorporate light-conducting cables. However, the installation of such cables is expensive. Also of disadvantage is the fact that the optical indicator of the monitoring arrangement remains illuminated for as long as the monitored electrical device is in order. This has proved to be of disadvantage in particular in the case of monitoring arrangements provided in automotive vehicles.